1. Field of the Invention
This invention relates to a slamming-resistant sonar dome canoe, and to a method for its manufacture.
2. Description of the Prior Art
Underwater SONAR (abbreviated from "Sound Navigation and Ranging") is finding ever-increasing use in the fields of navigation, mapping, depth finding, fish finding, and detection of wrecks and, militarily, for the detection of enemy vessels. There are generally two types of SONAR as used by surface vessels, namely: hull-mounted systems, wherein an underwater sound transducer or array is attached to the hull of the vessel; and variable depth systems, wherein an underwater sound transducer or array is mounted in a body towed by the vessel. The present invention is concerned with hull-mounted SONAR systems.
In the case of hull-mounted SONAR, it is usual to house the transducer or array of transducers in a streamlined, acoustically-transparent housing attached to the surface vessel. The purpose of this streamlined housing is to minimize the interfering effects of water flow noise around and adjacent to the transducer or array as the vessel moves through the water. In addition to streamlining the housing around the sides of the transducer, it is also usual to add a streamlined cover beneath. This cover is colloquilly known as a "canoe" because of the general resemblance in shape to that type of craft.
Mounting of the SONAR unit in a forward location (even precisely right at the bow) of the vessel is commonplace. Because it is sometimes necessary for divers to detech the canoe underwater for access to, and for servicing of, the underwater transducer or array, it is desirable that the canoe be light and easily handled.
In high seal states, it is usual that the stem of the vessel will alternately emerge from, then submerge again into, the sea. This gives rise to high momentary pressures, called "slamming pressures", beneath the stem. These pressures are repetitive, and since they can reach several hundred pounds per square inch, can be destructive both to the vessel and to any appendages thereon. The canoes of forward and bow mounted SONAR are directly subjected to these pressures, and must therefore be made robust to withstand them.
The requirement for robustness is contradictory to the requirement for light weight. Various means have been used in the past to reconcile these conflicting requirements. These have included (but are not restricted to) the use of complicated steel reinforcing frameworks within an outer skin of glass fiber reinforced plastic. However, these solutions have not been entirely satisfactory due to their complexity and/or weight and did not adequately solve the total problem by meeting the conflicting requirements of robustness and lightweight.
Many patents have attempted to provide floating structures which were alleged to combine lightness with considerable strength and water-impermeability. Among them are:
(1) Canadian Pat. No. 567,360 issued Dec. 8, 1958 to Tanza Electric and Chemical Works, which taught the use of a plurality of plates forming the hull of a boat, the plates comprising water-impermeable solid plastic sheets enclosing a core of closed-cell cellular plastic material;
(2) Canadian Pat. No. 681,568 issued Mar. 3, 1964 to Dominion Rubber Company, which provided a boat made up of a laminate of a core of a cellular gum plastic material, a rigid sheet of solid gum plastic material united to each face of the core, and an outer protective adherent material film overlying the outer surface of the rigid sheets;
(3) Canadian Pat. No. 694,755 issued Sept. 22, 1964 to David Bloom, which provided a buoyant pontoon of foam plastic within which anchorage means were integrally implanted;
(4) Canadian Pat. No. 734,289 issued May 17, 1966 to Wesley K. Landes which taught the use of aircraft floats made up of a shell of glass fiber reinforced plastic material substantially completely filled with a buoyant closed-cell cellular material;
(5) Canadian Pat. No. 736,835 issued June 21, 1966 to Michael Sawchuk, which provided a surfboard construction consisting of hollow sections molded from a plastic material and filled with a buoyant cellular material;
(6) Canadian Pat. No. 817,100 issued July 8, 1969 to George A. Gust, which provided a watercraft formed of solid, homogenous polystyrene foam, provided with an elongated reinforcing member embedded in the body;
(7) Canadian Pat. No. 840,152 issued Apr. 28, 1970 to Leo M. Krenzler which provided a boat hull of an outer shell of stiff structural material and an inner web of flexible reversely contoured reinforcing material, and having its bilge and side areas filled with foamed plastic which also encases the inner web of reversely contoured reinforcing material;
and (8) Canadian Pat. No. 857,643 issued Dec. 8, 1970 to Walter Anderson, which provided a watercraft whose hull was made of glass fiber reinforced plastic material whose internal cavity was substantially filled with light flotation material.